Membrane Distillation of Oil-Contaminated Wastewater Using Novel Fouling-Resistant Janus Membranes

The hydrophobicity of conventional membranes in membrane distillation (MD) makes them vulnerable to fouling in the treatment of saline water containing organic compounds. We prepared novel Janus MD membranes that possess excellent oil-fouling resistance using asymmetric vapor deposition of nanocoatings on liquid-infiltrated membranes. The solvent-free deposition provides a route to circumvent the obstacle of wettability incompatibility between processing hydrophilic and omniphobic polymers in solution phase. The deposition method also enabled processing of ultra-thin and conformal coatings into membrane microstructures without blocking membrane pores, leading to the maximal retention of membrane permeability. The depth of asymmetric modification can be tuned by adjusting the liquid infiltration and played a dual role in affecting the MD permeate flux. The novel Janus membrane enabled resistance to oil fouling at oil concentration as high as 5 g/L, while the traditional hydrophobic membrane and the advanced omniphobic membrane were completely fouled at oil content of 0.5 g/L and 2 g/L, respectively. MD desalination using the hypersaline produced water as the feed solution was performed. The high salt rejection of over 99.99% and stable permeate flux exhibited by the Janus membrane demonstrated the great potential in transforming MD desalination for water reclamation from oil-contaminated wastewater.